This application is related to a copending and simultaneously filed application of the same title and same inventor and identified by Ser. No. 043,577 filed May 29, 1979.
The present invention relates to an apparatus for short-arc welding of the kind which includes a controllable current source, means for controllably feeding a wire-like consumable electrode comprising additive material to the weld location, and a control unit for automatically adjusting the current source in dependence upon the welding sequence, said current source being arranged to provide welding periods divided into short-circuit intervals, arc intervals and optionally also rest intervals.
In short-arc welding operations, the additive material is fed to the welding zone in the form of a continuously advanced wire through which the welding current also flows. One characteristic of short-arc welding is that the wire electrode is brought into direct contact with the weld location at closely following points of time, so-called short-circuit intervals, and short circuits the welding current circuit until the outermost end of the wire has melted. Each short-circuit interval is followed by a so-called arc interval, during which an arc burns between the outermost end of the wire and the weld location. The arc interval can be interrupted, either spontaneously as a result of the arc being extinguished due to the wire again short circuiting the said current circuit, or because the power is too low to maintain the arc, or the arc may be extinguished positively by automatically interrupting the supply of current by means of a control unit for the current source prior to the entry of the short-circuiting state. In the two latter cases there is obtained a so-called rest interval, during which current to the weld location is broken. The short-arc welding sequence is thus pulse-like or periodic, each welding period comprising a short-circuit interval and an arc interval, and optionally also a rest interval.
When short-arc welding, it is necessary to be able to adjust the supply of additive material in dependence upon the welding conditions, including the nature of the objects to be welded. However, one problem encountered with short-arc welding apparatus used until now has been that variations in the supply of additive material require the parameters of the current source to be adjusted, which adjustments have hitherto been made manually, there being required a degree of expertise on the part of the welder if optimal weld results are to be obtained. In addition there has been used in certain cases means for measuring the speed at which the wire-electrode feeding device operates to feed the additive wire to the weld location, and to automatically compensate the setting of the current source in response to the measured speed. However, as a result of slipping and other disturbances in the wire-feeding device, momentary variations may occur in the supply of additive material during a welding operation, these variations and interruptions being harmful to the weld result and rendering it impossible to continuously correct the source of welding current, either manually or with the automatic devices hitherto used.